1. Technical Field
The present invention relates in general to the transmission of data frames between local area networks (LANs) and in particular to a system for transmitting LAN data frames through an asynchronous transfer mode (ATM) crossbar switch.
2. Description of the Related Art
Local area networks (LANs), such as ethernet or token-ring networks, are generally coupled via hubs. A hub is a system made of LAN adapters that communicate via a switch card. This switch card is implemented either as a parallel bus or a passive switch card, which further includes a matrix for achieving the connection between selected inputs and outputs.
Today, asynchronous transfer mode (ATM) technology is improving at a rapid rate. Most research developments in this field are concentrated in high-speed ATM networks instead of LANs. Extremely high speed ATM switches are now readily available and are utilized for transferring data between LANs coupled to the ATM switch. The utilization of the ATM technology for switching LAN frames requires a transformation of each LAN frame by splitting the LAN frame into ATM frames. This is accomplished by encapsulating each LAN frame in the ATM adaptation layer (AAL) format.
The LAN frame is transformed into ATM data packets in the AAL format via a special module. The LAN frame is then transferred to the switch card for switching. Such a requirement results in two major drawbacks. Since the frame is converted into ATM cells, a header in each cell including protocol information (e.g., destination address) is required. A second drawback is that the transformation of the LAN frame into ATM cells and the encapsulation in the AAL format requires important and costly hardware and software.
When a first LAN adapter requests transmission of a LAN frame to a second LAN adapter, the first LAN adapter sends a requests to the ATM switch and a scheduler determines whether or not satisfying this request is possible, while considering an algorithm that determines the best data coupling to establish at each time. Accordingly, the grant signal to this request may be delayed before being returned to the requesting LAN adapter, while other requests are still waiting to be processed in the second LAN adapter.
Consequently, it would be desirable for a system for exchanging data between multiple LANs without delaying requests between LANs.